Acoustic material



Aug. 17, l943.` D. D. QRANDELL l 2,325,763

ACOUSTIC MATERIAL Filed June 28, 1939 SOUND ABSORB/NG BCOY /L /MPERV/OUS COA TNG u o o o o o o o a u u o u o o o o n u o a D n n n o o o uo a o e e v o o o a a u u u u o DEcoRAT/VE n o a u n u n o COA TNG o o no n n n o n o u a n o o c n o o o Q c o o o INV'ENTOR ATTORNEYS PatentedAug. 17, 1943 ACOUSTIC MATERIAL Dean D. Crandell, Buffalo, N. Y.,assignor to National Gypsum Company, Buialo, N. Y.

Application June 2-8, 1939, Serial No. 281,663

1 Claim. (Cl. 15de-44) This invention relates to an acoustical material.

Various materials and compositions of materials have heretofore beenproposed for the production of sound proof or sound absorbent walls forbuilding construction and the like. While various objections have arisento hitherto known constructions, a prime difiiculty has been the problemof decoration since it has either been impossible to paint or otherwisedecorate or redecorate the surface of the material after erection of thebuilding, or such painting or decoration could be accomplished only tothe impairment or utter destruction of the sound absorbing or soundproofing qualities ofthe structure.

The present invention produces and provides an acoustic material,generally in the form of a slab-like wall element, the exposed surfaceof which may be painted, either by brushing or spraying, not onlyimmediately after completion of the wall construction, but subsequently,as often as desired, without in any way destroying or reducing theoriginal acoustical qualities of the wall.

This result is lachieved by providing as a base or body for theacoustical element a block or slab of a highly sound absorbent material.In the form of the invention which is disclosed herein as beingillustrative of the principles thereof I employ a self-sustaining slabof relatively low density fiber board, the same being conventionallyformed from wood pulp or other cellulosic fibrous material.

To this base I apply, either by spraying or brushing or in anyconvenient manner, a coating prepared by mixing an adhesive, usually` anorganic glutinous or starchy material with whiting or other pulverantchalky substance with sufcient liquid to form a slurry. Afterapplication the coating is permitted to harden and dry thoroughlywhereuponthe coating is perforated by the formation of relativelyshallow holes in the coated surface of the element, usually bysimultaneously piercing the'coating at a number of points. Such piercingof the coating is found to permit sound waves to have access to theexposed sound deadening or absorbing material to a sufficient extent toabsorb approximately the same per cent of sound as the same soundabsorbing material absorbs when not provided with the finish taught bymy present invention.

In the accompanying drawing:

Fig. 1 is a front or face view of an element adapted to be used as anexposed wall element and constructed in accordance with. the principlesof my invention, tne several areas of the element being shown toindicate diagrammatically the several steps or operations which comprisemy new method of producing an acoustic wall element;

Fig. 2 is a similar vie'w showing the finished element fragmentarily andon an enlarged scale with respect to Fig. 1; and,

Fig. 3 is a fragmentary cross sectional view, on a still furtherenlarged scale, showing the relatively impervious ,coating and theperforations therethrough.

In Fig. 1 of the drawing the four zones displayed indicate, readingfromtop to bottom, four conditions of the building element occurringserially during the production of the element. The top zone representsthe initial untreated block or slab of fibrous material having a highdegree of sound and liquid absorption. The next zone represents theblock after it has been coated with the relatively impervious coatingreferred to heretofore. The third zone shows the block afterperforations have been formed through the 'coating and in fact shows thecompleted building element, ready to be incorporated in a building Walland subsequently decorated in any conventional manner Without having itseiciency as a sound absorbing elementl affected in any way. The fourthzone shows the block as it appears after it has been incorporated in awall construction and decorated as indicated.

The body of sound absorbing material is designated at l0 in the drawingand in its preferred form comprises what is known in the building art aslow density fiber board. This board is conventionally formed bysubjecting wet wood pulp or other cellulose fiber pulp to pressure,usually at elevated temperatures. The slabs so .formed are of lowdensity but are sufficiently compact to be self-sustaining andsufiiciently strong and rigid as to be conveniently handled withoutliability of breakage or disintegration.

Another property of low density ber board is its very high soundabsorption. 'I'his quality makes its use as an acoustic material highlyadvantageous but in the past a marked objection to its use has residedin the fact that it is next to impossible to coat the material becauseof its very strong tendency to absorb liquids. Again, even if suiiicientpaint or the like were applied to form a coating, or if a sufficientlythick material were applied with like result, the board would then loseits sound absorbing quality.

In pursuing my invention I so treat the body of sound insulatingmaterial as to not destroy 4its sound absorbing-'ability while making itpossible lto apply conventional wall finishes such as paint andthe liketo its surface. In proceeding to accomplish thisaim I prepare a slurryor dispersion which in the preferred form comprises an. adhesive orAbindingmaterial which may be starch, casein, soybean flour,v glue, orother material having the indicated properties together with aninorganic ller such as Whiting, precipitated chalk, marl, light-weight;gypsum, .or the like.

\ As specific examples, I may employ an aqueous dispersion which in thedry state comprises soya bean protein' and 90% ller or a dispersion of50% starch and 50% whiting. i A coating of the dispersion so formed mayreadily be sprayed or brushed upon a surface of the sound absorbing bodyand is found to form a layer which is sufficiently impermeable to thevehicles used in conventional paints, of both -the oil and watervariety, as to' satisfactorily meet the requirements of the presentinvention. In the drawing the coating is designated l I.

After the coating has thoroughly dried, I form perforationstherethrough. Such perforations are desired to be wholly through thecoating but l extend as little as is practically possible into the bodyof the sound absorbing material itself. As to size, a prime requisite isthat the opening so formed be of sufcient diameter or distance across asnot to be closed or bridged over by a subsequent painting operation whensuch paint is applied either by spraying or brushing. It is found thatopenings approximately alf in diameter give results quite satisfactoryfrom this standpoint.

In the illustrated example, the openings designated at i2 in the drawingare uniformly distributed over the coated surface of the board and insuch example I have shown the openings so spaced that they occurapproximately seven to the square inch.

The lower zone of Fig. 1 represents the block or board I0 after it hasbeen incorporated in a wall structure andprovided with one or moresurface coatings of paint as at I3.

the art of sound deadening and sound insulation particularly. Y

While specific examples ofthe general principle involved in thisinvention have been referrea to herein, it is tobe understood that afull range of equivalents is in contemplation and that suchmodifications as appear to those skilled in the art jmay be made withoutdeparting from the spirit and scope of my invention as dened in theappended claim I claim:

An acoustic construction comprising a body of low density, compacted,cellulosic fibrous material having a surface thereof coated with amaterial relatively impervious topaint vehicles and comprising adispersion of protein and an inorganic ller, said coating being friableby nature and provided with a plurality of perforations whereby theunderlying brousmaterial *is par- -without closing or filling saidopenings and being of a total depth only slightly greater than thethickness of said coating.

=DEAN D. CRANDELL.

